CROWN: A Service Grid Middleware for e-Science - Grid Computing: Infrastructure, Service, and Applications - page 24

requirement. At i rst, a user would use a CredMan client command, named
credman-init , to visit the CredManService and delegate a set of proxy creden-
tials that are signed by the user's permanent credential to the service reposi-
tory. At a later time when the user's credential is needed, the user, or the
service acting on behalf of the user, gets a proxy credential delegated from
the proxy credential stored in the repository.
In CROWN, client tools can be integrated with the portal; that is, a user
can access his credential through the portal. By using the tools, a user can
easily delegate to and retrieve credentials from the repository. Moreover,
some client tools are provided for the user to manage the credentials
stored in the repository. In order to protect the credentials in the service
repository, CredManService provides a protected mechanism in which a
user can specify authentication information and retrieval restrictions to
protect his credentials in the repository.

1.4.2.5 Trust Management and Negotiation

A dedicated ATNService can be deployed with the target service to support
the trust negotiation with the service requestor. As illustrated in Figure 1.12,
a series of procedures are involved in the trust negotiation. When the client
requests the target service, which is protected by the trust negotiation serv-
ice, it will i rstly initialize an ATNEngine through a local RedirectHandler .
Upon receiving the negotiation request from a client, the service provider
will create an ATNEngine , too. The state of negotiation will be stored in
ATNContext . Then, the two participants may disclose their credentials
according to the provider's policy or policies for sensitive credentials. This
process will be interacted until a i nal decision (“success” or “failure”) is
reached. If the negotiation succeeds, ATNService will return a success
status, and the context will be updated accordingly. The requestor can insert

Trust ticket
manager

Creds Policy

Control flow
Data flow

ATN
Engine

Negotiation
strategy

Trust chain
construction
ATNEngine

ATN
Service

Config

ATN
Engine

ATN
Context

Target
service

RedirectHandler

AuthzHandler

Config Service provider

Config

Service requestor

Domain boundary

FIGURE 1.12 ATNService and ATNEngine.